1. Field of the Invention
The present invention relates to a pipe joint, and more particularly to a pipe joint having a socket which, even when a pipe inserted therein is inclined with respect to the axis thereof, can prevent the pipe and joint from being subjected to excessive stresses or breakage and can also prevent a rubber ring seal mounted therein from being easily dislocated or slipping off due to internal pressures.
2. Description of the Prior Art
Typical examples of the conventional pipe joint provided with an annular groove for receiving a rubber ring seal will be hereinafter described with reference to FIGS. 1 to 6, which are longitudinal sectional views of the examples, respectively, of the conventional pipe joint shown with a pipe inserted in the socket thereof.
In all of these examples, the clearance between the internal surface of the socket and the outside surface of the pipe inserted in the socket is made as small as possible at sections X--X', Y--Y', Z--Z', W--W', etc., so that accidents such as water leakage may not occur which may be caused by dislocation or slipping-off of the rubber ring seal from the groove due to internal pressures in the pipe joint. For this reason, the allowable limit of the pipe inclination necessary and very significant for the pipe joint is inevitably limited to a very small value. In the case of the conventional pipe joint having such a relationship between the shape, dimension, etc., of the socket and those of the inserted pipe as shown in FIGS. 1 to 6, in fact, the inserted pipe when actually in use is subjected to a levering action in the socket and thereby is exposed to high pressures at portions in point contact even when slightly inclined with respect to the axis of the socket or joint. In this case, the pipe inserted in the socket and inclined with respect to the axis thereof tends to be strongly pressed against the internal surface of the socket at the side on Section Y--Y' toward which the pipe is inclined. As a result, the portions in point contact are subjected to large stresses and deformations; and, in addition, the clearance between the internal surface of the socket and the outside surface of the pipe inserted in the socket and inclined with respect to the axis thereof becomes larger at the side on Section Y--Y' opposite to which the pipe is inclined, until it reaches a value almost corresponding to the difference between the inside diameter of the socket and the outside diameter of the inserted pipe. The occurrence of such a large clearance (refer to JIS B 2406-1967, page 25, FIG. 9: Explanation of the shape and size of the O-ring groove) tends to cause the rubber ring seal in the groove to be easily dislocated or slip off passing through the above large clearance due to internal pressures in the socket. Consequently, the pipe joint of this type is usually compelled to take a form as shown in FIG. 6, in which the clearance between the inside surface of the socket and the outside surface of the inserted pipe is made as small as possible. The examples of such a pipe joint can be clearly seen from the standard of the shapes, dimensions, dimensional tolerances, etc., of pipe joints and the appended drawings set up by the Japan Polyvinyl Chloride Tubing and Pipe Joint Association on Apr. 22, 1974 concerning hard polyvinyl chloride RR single-supported straight pipes for aqueduct, hard polyvinyl chloride RR specials for aqueduct, cast iron RR specials for hard polyvinyl chloride pipes for aqueduct, etc.
However, the pipe joint of this type has various advantages in use and operation in spite of the above disadvantages.
Accordingly, all the related manufacturers and users have been eagerly hoping for the advent of an improved pipe joint that can satisfactorily prevent the occurrence of extraordinarily great stresses therein or breakage thereof, dislocation or slipping-off of the rubber ring seal from the groove formed therein, etc., even if the inserted pipe is inclined at 4.degree. to 5.degree. with respect to the axis of the socket.